More than a thousand people have been injured after a tsunami - caused by the eruption of the Anak Krakatau volcano - struck coastal areas between Sumatra and Java islands on Saturday night, officials say.

An aerial photo shows damaged buildings in Carita on December 23, 2018, after the area was hit by a tsunami on December 22.
(AFP)

The death toll from an Indonesian tsunami has risen past 370 with more than 1,400 people injured.

The Indonesia disaster agency raised the death toll to at least 373 on Monday. That number could rise further, with 128 people still missing, agency spokesman Sutopopurwo Nugroho said.

The tsunami struck Sunda Strait coastal areas along western Java and southern Sumatra islands without warning in the darkness of Saturday night.

TRT World's Ben Tornquist reports.

Scientists say the tsunami could have been caused by the eruption of Anak Krakatau, a volcanic island formed over years from the nearby Krakatau volcano.

They also cited tidal waves caused by the full moon.

The areas that were affected were South Lampung in Sumatra and the Serang and Pandeglang regions of Java, west of the capital Jakarta.

The Sunda Strait between the islands of Java and Sumatra connects the Java Sea to the Indian Ocean.

Pacific 'Ring of Fire'

Indonesia, one of the most disaster-prone nations on earth, straddles the so-called Pacific 'Ring of Fire', where tectonic plates collide and a large portion of the world's volcanic eruptions and earthquakes occur.

The country regularly experiences deadly earthquakes, including most recently in the city of Palu on Sulawesi island where a quake and tsunami killed thousands of people.

Anak Krakatau is one of 127 active volcanoes which run the length of the archipelago.

Indonesian authorities initially claimed the wave was not a tsunami, but instead a tidal surge and urged the public not to panic.

Nugroho later apologised for the mistake on Twitter, saying because there was no earthquake it had been difficult to ascertain the cause of the incident early on.

"If there is an initial error we're sorry," he wrote.

Rescue and relief underway

The wave swamped parts of the coast around the Sunda Strait, but was most damaging in Pandeglang district, on Java's western tip, where at least 33 people died and 491 people were injured.

Three people died further north in Serang, while seven were killed in South Lampung, on Sumatra island.

Heavy equipment was being transported to badly-hit areas to help search for victims, Nugroho said, adding evacuation posts and public kitchens were being set up for evacuees.

Abu Salim, a member of the Tagana disaster volunteer group, said he helped evacuate victims in Banten province.

"We evacuated the victims who died and were injured, we took them to health clinics ... Most of them suffered from broken bones," he said, adding he feared more were missing.

Turkey condoles deaths

Although relatively rare, submarine volcanic eruptions can cause tsunamis due to the sudden displacement of water or slope failure, according to the International Tsunami Information Centre.

Anak Krakatoa is a small volcanic island that emerged from the ocean half a century after Krakatoa's deadly 1883 eruption which killed more than 36,000 people.

Turkish President Recep Tayyip Erdogan on Sunday offered his condolences over the deadly tsunami.

"In the name of the Turkish people I hereby express our condolences to all the people of Indonesia," he said during the Financial General Assembly 2018 meeting of Foreign Economic Relations Board (DEIK) in Istanbul.